Regulatory Matters - Regulatory Assets and Liabilities (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Regulatory assets
Regulatory assets - long-term	$ 7,201.0	$ 9,705.0
Regulatory assets - current	29	74
Total Regulatory Assets	7,230	9,779
Regulatory liabilities
Regulatory liabilities - long-term	1,728	1,202
Regulatory liabilities - current	148	183
Total Regulatory Liabilities	1,876	1,385
Unrecognized Pension and Other Postretirement Costs [Member]
Regulatory assets
Regulatory assets - long-term	2,730.0	5,677.0
Future Income Tax [Member]
Regulatory assets
Regulatory assets - long-term	2,145.0	1,922.0
Environmental Remediation Costs [Member]
Regulatory assets
Regulatory assets - long-term	938.0	730.0
Deferred Storm Costs [Member]
Regulatory assets
Regulatory assets - long-term	441.0	432.0
Pension and Other Postretirement Benefits Deferrals [Member]
Regulatory assets
Regulatory assets - long-term	237.0	183.0
Revenue Taxes [Member]
Regulatory assets
Regulatory assets - long-term	207.0	176.0
Net Electric Deferrals [Member]
Regulatory assets
Regulatory assets - long-term	83.0	102.0
Surcharge for New York State Assessment [Member]
Regulatory assets
Regulatory assets - long-term	78.0	73.0
Unamortized Loss on Reacquired Debt [Member]
Regulatory assets
Regulatory assets - long-term	65.0	74.0
O&R Transition Bond Charges [Member]
Regulatory assets
Regulatory assets - long-term	33.0	39.0
Preferred Stock Redemption [Member]
Regulatory assets
Regulatory assets - long-term	28.0	29.0
Property Tax Reconciliation [Member]
Regulatory assets
Regulatory assets - long-term	22.0	16.0
Regulatory liabilities
Regulatory liabilities - long-term	322	187
Workers' Compensation [Member]
Regulatory assets
Regulatory assets - long-term	12.0	19.0
Deferred Derivative Losses - Long-Term [Member]
Regulatory assets
Regulatory assets - long-term	8.0	40.0
Other [Member]
Regulatory assets
Regulatory assets - long-term	174.0	193.0
Deferred Derivative Losses - Current [Member]
Regulatory assets
Regulatory assets - current	25	69
Recoverable Energy Costs - Current [Member]
Regulatory assets
Regulatory assets - current	4	5
Allowance for Cost Removal Less Salvage [Member]
Regulatory liabilities
Regulatory liabilities - long-term	540	503
Net Unbilled Revenue Deferrals [Member]
Regulatory liabilities
Regulatory liabilities - long-term	133	136
Regulatory liabilities - current	133
Property Tax Refunds [Member]
Regulatory liabilities
Regulatory liabilities - long-term	130	7
Long-Term Interest Rate Reconciliation [Member]
Regulatory liabilities
Regulatory liabilities - long-term	105	62
Carrying Charges On Repair Allowance And Bonus Depreciation [Member]
Regulatory liabilities
Regulatory liabilities - long-term	88	11
World Trade Center Settlement Proceeds [Member]
Regulatory liabilities
Regulatory liabilities - long-term	62	62
Other Postretirement Benefit Deferrals [Member]
Regulatory liabilities
Regulatory liabilities - long-term	50
Expenditure Prudence Proceeding [Member]
Regulatory liabilities
Regulatory liabilities - long-term	40	14
Carrying Charges on Transmission and Distribution Net Plant [Member]
Regulatory liabilities
Regulatory liabilities - long-term	28	31
Electric Excess Earnings [Member]
Regulatory liabilities
Regulatory liabilities - long-term	22
Other [Member]
Regulatory liabilities
Regulatory liabilities - long-term	208	189
Refundable Energy Costs - Current [Member]
Regulatory liabilities
Regulatory liabilities - current	100	82
Revenue Decoupling Mechanism [Member]
Regulatory liabilities
Regulatory liabilities - current	34	72
Deferred Derivative Gains - Current [Member]
Regulatory liabilities
Regulatory liabilities - current	14
Electric Surcharge Offset [Member]
Regulatory liabilities
Regulatory liabilities - current		29
CECONY [Member]
Regulatory assets
Regulatory assets - long-term	6,639.0	8,972.0
Regulatory assets - current	26	60
Total Regulatory Assets	6,665	9,032
Regulatory liabilities
Regulatory liabilities - long-term	1,598	1,077
Regulatory liabilities - current	107	145
Total Regulatory Liabilities	1,705	1,222
CECONY [Member] | Unrecognized Pension and Other Postretirement Costs [Member]
Regulatory assets
Regulatory assets - long-term	2,610.0	5,407.0
CECONY [Member] | Future Income Tax [Member]
Regulatory assets
Regulatory assets - long-term	2,030.0	1,831.0
CECONY [Member] | Environmental Remediation Costs [Member]
Regulatory assets
Regulatory assets - long-term	830.0	615.0
CECONY [Member] | Deferred Storm Costs [Member]
Regulatory assets
Regulatory assets - long-term	334.0	309.0
CECONY [Member] | Pension and Other Postretirement Benefits Deferrals [Member]
Regulatory assets
Regulatory assets - long-term	211.0	154.0
CECONY [Member] | Revenue Taxes [Member]
Regulatory assets
Regulatory assets - long-term	196.0	170.0
CECONY [Member] | Net Electric Deferrals [Member]
Regulatory assets
Regulatory assets - long-term	83.0	102.0
CECONY [Member] | Surcharge for New York State Assessment [Member]
Regulatory assets
Regulatory assets - long-term	74.0	68.0
CECONY [Member] | Unamortized Loss on Reacquired Debt [Member]
Regulatory assets
Regulatory assets - long-term	62.0	70.0
CECONY [Member] | Preferred Stock Redemption [Member]
Regulatory assets
Regulatory assets - long-term	28.0	29.0
CECONY [Member] | Property Tax Reconciliation [Member]
Regulatory liabilities
Regulatory liabilities - long-term	322	187
CECONY [Member] | Workers' Compensation [Member]
Regulatory assets
Regulatory assets - long-term	12.0	19.0
CECONY [Member] | Deferred Derivative Losses - Long-Term [Member]
Regulatory assets
Regulatory assets - long-term	7.0	20.0
CECONY [Member] | Other [Member]
Regulatory assets
Regulatory assets - long-term	162.0	178.0
CECONY [Member] | Deferred Derivative Losses - Current [Member]
Regulatory assets
Regulatory assets - current	22	60
CECONY [Member] | Recoverable Energy Costs - Current [Member]
Regulatory assets
Regulatory assets - current	4
CECONY [Member] | Allowance for Cost Removal Less Salvage [Member]
Regulatory liabilities
Regulatory liabilities - long-term	453	420
CECONY [Member] | Net Unbilled Revenue Deferrals [Member]
Regulatory liabilities
Regulatory liabilities - long-term	133	136
CECONY [Member] | Property Tax Refunds [Member]
Regulatory liabilities
Regulatory liabilities - long-term	130	6
CECONY [Member] | Long-Term Interest Rate Reconciliation [Member]
Regulatory liabilities
Regulatory liabilities - long-term	105	62
CECONY [Member] | Carrying Charges On Repair Allowance And Bonus Depreciation [Member]
Regulatory liabilities
Regulatory liabilities - long-term	87	10
CECONY [Member] | World Trade Center Settlement Proceeds [Member]
Regulatory liabilities
Regulatory liabilities - long-term	62	62
CECONY [Member] | Other Postretirement Benefit Deferrals [Member]
Regulatory liabilities
Regulatory liabilities - long-term	50
CECONY [Member] | Expenditure Prudence Proceeding [Member]
Regulatory liabilities
Regulatory liabilities - long-term	40	14
CECONY [Member] | Carrying Charges on Transmission and Distribution Net Plant [Member]
Regulatory liabilities
Regulatory liabilities - long-term	20	13
CECONY [Member] | Electric Excess Earnings [Member]
Regulatory liabilities
Regulatory liabilities - long-term	18
CECONY [Member] | Other [Member]
Regulatory liabilities
Regulatory liabilities - long-term	178	167
CECONY [Member] | Refundable Energy Costs - Current [Member]
Regulatory liabilities
Regulatory liabilities - current	66	48
CECONY [Member] | Revenue Decoupling Mechanism [Member]
Regulatory liabilities
Regulatory liabilities - current	30	68
CECONY [Member] | Deferred Derivative Gains - Current [Member]
Regulatory liabilities
Regulatory liabilities - current	11
CECONY [Member] | Electric Surcharge Offset [Member]
Regulatory liabilities
Regulatory liabilities - current		$ 29